Part 68 (1/2)

The chief difficulty is to exclude the possible existence of a cerebellar abscess (see p. 460). In favour of labyrinthine inflammation is complete internal-ear deafness, although this in itself does not exclude an accompanying intracranial lesion.

1. _Immediate exploration of the labyrinth is indicated_ (provided there is internal-ear deafness):--

(_a_) If symptoms of _acute_ labyrinthine suppuration occur in the course of a middle-ear suppuration, even although at the time of opening of the mastoid no definite fistula of the labyrinthine wall can be discovered.

(_b_) If symptoms of involvement of the labyrinth be present and a definite fistula is found on operation.

(_c_) If symptoms of a cerebellar abscess or of meningeal irritation be present in addition to those suggestive of a labyrinthine affection.

2. _Opening of the labyrinth should be delayed_ if Barany's and other tests show that the labyrinth is not yet destroyed:--

(_a_) If, in spite of clinical symptoms pointing to involvement of the labyrinth, pus be found under tension within the tympanic cavity or the mastoid process.

(_b_) If the symptoms before operation consist only of attacks of vertigo and nystagmus, and on operation merely an erosion of the outer wall of the labyrinth (usually the external semicircular ca.n.a.l) is discovered.

In the above cases, if the symptoms be due to irritation of the labyrinth, a rapid recovery is to be expected as a result of the mastoid operation. If, however, they continue or become progressively worse, then the wound cavity must be reopened and the labyrinthine wall carefully examined and further operation undertaken.

The reader may again be reminded that although exploration of the labyrinth is indicated when it is certain that a suppurative lesion exists, yet it is a very serious mistake to open up a labyrinth not yet infected.

Although a great advance has been made in the last few years with regard to operations on the labyrinth, yet there is still much to be learnt, not only with regard to the indications for operation but the result obtained by operation. Now that operations on the labyrinth have become universal, the general tendency is to operate on the immediate occurrence of symptoms of labyrinthine irritation without waiting to see whether simple opening of the mastoid process will not be sufficient--a matter much to be regretted.

=Surgical Anatomy.= The facial ca.n.a.l, it will be remembered, extends horizontally backwards above the promontory, and pa.s.ses downwards superficially to the inferior portion of the vestibule which lies between the fenestra ovalis below and ampullary ends of the external and superior semicircular ca.n.a.ls above. The nerve then extends directly downwards towards the stylo-mastoid foramen, being situated deeply within the posterior meatal wall.

Of the semicircular ca.n.a.ls the external is the most prominent, and the only one visible during the performance of the ordinary mastoid operation; its outer border forms the inner and lower boundary of the aditus, and can usually be recognized as a white eminence. The superior semicircular ca.n.a.l can only be seen on careful removal of the overlying bone; its ampullary end is found lying just above that of the external ca.n.a.l. It forms the highest point of the labyrinth, becoming fused with the innermost portion of the tegmen tympani, and is in such close relations.h.i.+p with the upper surface of the petrous bone as to cause a smooth elevation on its surface. It is at this point in the operation of removal of the semicircular ca.n.a.l that the greatest risk is encountered of breaking through the petrous bone and of injuring the dura mater.

The posterior semicircular ca.n.a.l lies at right angles to the external ca.n.a.l, and is best exposed by careful removal of bone just posterior to the latter (see Fig. 240).

The outer half of the first whorl of the cochlea is formed by the promontory. Anteriorly it is in close relations.h.i.+p with the carotid ca.n.a.l, whilst below it lies the dome of the jugular fossa. Medially the modiolus is only separated from the internal auditory meatus by a very fine rim of brittle bone, which can easily be broken; a mishap which may permit of escape of the cerebro-spinal fluid, and also of possible infection of the meninges through the internal meatus.

METHODS OF OPERATING

These operations may be divided into: (1) simple curetting away of a localized lesion of the labyrinthine wall; (2) opening up of the vestibule with removal of the semicircular ca.n.a.ls; (3) opening of the cochlea; (4) a combination of these methods--extirpation of the labyrinth.

=Curetting away of a localized lesion of the labyrinthine wall.= It has been already stated that, provided the labyrinth be not yet destroyed, it is not justifiable to explore it on the mere discovery of an erosion of the semicircular ca.n.a.l. At the same time, if a definite fistula from which granulations protrude is present, a small fragment of bone may be chipped away, the granulations being afterwards removed by the curette.

Unless pus is found to exude from the labyrinth, it is not necessary to do anything further at the present moment. If, however, at a later period, symptoms of labyrinthine infection occur, then it is necessary to further explore the semicircular ca.n.a.l and vestibule, the extent of the operation depending on what is discovered at the time of the operation.

Sometimes an examination of the tympanic cavity may be prevented before operation owing to the auditory ca.n.a.l being filled with polypi or granulations. On performing the complete mastoid operation and curetting away these granulations and polypi, a fistula may be found in the promontory, and carious bone may be felt on probing. Not infrequently these cases are tuberculous in origin and are accompanied by facial paralysis. Provided there be no labyrinthine symptoms, it is sufficient to curette out the granulations, but only gently. Violent curetting may break through the barrier between the infected area and the internal meatus and so lead to meningitis. It is wiser to curette too little than too much.

A further condition which may be met with is necrosis of a portion of the promontory, or of the walls of the vestibule, or of the semicircular ca.n.a.ls. If the sequestrum be not quite loose at the time of operation, it should be left _in situ_, provided there be no intracranial symptoms.

In fact, there is less danger in leaving the sequestrum than in attempting to remove it. After the operation, the wound cavity is kept open, so that the sequestrum can be removed at a later date after it has separated from the living bone.

=Opening the vestibule= (with partial or complete removal of the semicircular ca.n.a.ls). This may be performed by one of the following methods:--

_Above and behind the facial nerve through the semicircular ca.n.a.ls._ The complete mastoid operation is performed first. The chief difficulty is to expose the field of operation so as to obtain sufficient room for the necessary manipulations. To do this the following steps should be carried out: The tip of the mastoid process and the remains of the posterior wall of the auditory ca.n.a.l are removed to their extreme limit without injury to the underlying facial nerve. The floor of the auditory ca.n.a.l is also chiselled away until the lower level of the tympanic cavity is brought freely into view, the amount of bone removed depending on the anatomical condition found. To expose the anterior portion of the tympanic cavity, the skin incision is extended slightly forwards, but not far enough to wound the temporal artery, the soft tissues being then separated from the bone and the auricle pulled still further forwards and downwards.

Skin meatal flaps are now fas.h.i.+oned--either the Y-shaped flap or Stacke's flap (see p. 403)--and are afterwards kept in position by means of sutures. Good illumination is necessary, and for this reason a head-light should be used. One a.s.sistant is employed to retract the soft tissues from the wound, another to keep it as dry as possible.

The exposed portion of the external semicircular ca.n.a.l is first identified. If the bone be soft, the arches of the semicircular ca.n.a.l should be defined (Fig. 240). The posterior ca.n.a.l will be discovered by gouging away the bone just posterior to the arch of the external semicircular ca.n.a.l, and the superior, by working inwards and upwards towards the roof of the attic. If the outline of the ca.n.a.ls can be made out, the further steps of the operation are rendered very much easier.

Unfortunately, the bone is sclerosed in the majority of cases, rendering anatomical exposure of the ca.n.a.ls an impossibility.